1. Field of the Invention
The present invention relates to a waveguide filter provided with coaxial/waveguide mode conversion parts for converting a transmission mode between a coaxial and a waveguide, in One or both ends thereof.
2. Description of the Related Art
A waveguide filter one or both ends of which are to be coupled through coaxial lines to other circuit elements is provided with coaxial/waveguide mode conversion parts in one or both ends thereof. In an end of the waveguide filter where the coaxial/waveguide mode conversion part is provided, the waveguide is sealed by inserting a metal block into an open end of the waveguide and by screwing the waveguide on the metal block.
Though a cross section of the metal block is made so as to fit a cross section of a space bounded by the waveguide in order to prevent leakage of electric waves, gaps tend to be formed between the metal block and inner walls of the waveguide because of deflection of the walls of the waveguide that are not secured by screws, and filter loss tends to be increased because of leakage of the electric wave through the gaps. Though conductive adhesive or copper foil has been used to fill the gaps, attenuation of the leaked electric waves is limited to about 60 dB. Thus, it has been difficult and costly to reduce the leakage to a desired level.